Questions On 740 Fan w/2-spd Relay

2JZFC · 02-12-2021, 10:29 AM

Greetings.

What is the maximum amperage draw for this unit, accounting for kick-on and hi-speed?

If the 2-spd relay unit's power source is fused SW12V coming from a distribution block, is another relay necessary?

TIA

bobxyz · 02-12-2021, 04:24 PM

I'm not familiar with 740s or 940s, but on a 240, the extra fan just for added A/C cooling is fused off the battery at 20amps. I'd guess a dual fan for primary cooling would need 50amps, or more.

You definitely do NOT want to connect the main fan power to switched +12v, or you'll burn up the ignition switch. Flipping though some 940 wiring diagrams, those fans are powered directly from the battery junction block, or maybe through a fusible link, but no fuses. The relay coil circuits are low power and come from switched +12v.

Lankku · 02-12-2021, 08:03 PM

700/900/850/x70I 2-speed fan relay is ground controlled and has constant 12V. Full speed takes around 30A when it's switched on directly. Depending on stuff it's a bit under or over. So if low speed is always switched on first then 30A is enough.

2JZFC · 02-13-2021, 12:31 AM

Thanks, guys.

02-12-2021, 10:29 AM	#1
2JZFC Board Member Join Date: Feb 2018 Location: Orlando, FL	Questions On 740 Fan w/2-spd Relay Greetings. What is the maximum amperage draw for this unit, accounting for kick-on and hi-speed? If the 2-spd relay unit's power source is fused SW12V coming from a distribution block, is another relay necessary? TIA

02-12-2021, 08:03 PM	#3
Lankku Board Member Join Date: May 2015 Location: Finland	700/900/850/x70I 2-speed fan relay is ground controlled and has constant 12V. Full speed takes around 30A when it's switched on directly. Depending on stuff it's a bit under or over. So if low speed is always switched on first then 30A is enough. __________________ 444 -55, 242 DL -80 (was 4.6l)sold, 245 -88 "B6284T" sold, 245 -92 B6294, 245 -90 "B6284T"

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

02-12-2021, 04:24 PM	#2
bobxyz Board Member Join Date: Aug 2014 Location: Boulder CO	I'm not familiar with 740s or 940s, but on a 240, the extra fan just for added A/C cooling is fused off the battery at 20amps. I'd guess a dual fan for primary cooling would need 50amps, or more. You definitely do NOT want to connect the main fan power to switched +12v, or you'll burn up the ignition switch. Flipping though some 940 wiring diagrams, those fans are powered directly from the battery junction block, or maybe through a fusible link, but no fuses. The relay coil circuits are low power and come from switched +12v.

02-13-2021, 12:31 AM	#4
2JZFC Board Member Join Date: Feb 2018 Location: Orlando, FL	Thanks, guys.